A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine, including fueling of the engine by injection of fuel into engine combustion chambers. Control of engine fueling involves various considerations, one of which is controlling the pressure at which fuel is injected into the combustion chambers.
A diesel engine operates by the injection of fuel at relatively high hydraulic pressure. Hydraulic fluid under pressure, such as oil that is being pumped by an engine-driven oil pump to create a head pressure, is supplied to fuel injectors for use as the source of injection pressure. A fuel injector may amplify the head pressure, such by an intensifier piston, to inject a charge of fuel at a pressure corresponding to the product of hydraulic head pressure and intensifier piston amplification factor.
The head pressure of the oil is closely regulated, such as by a closed-loop control that continually seeks to null an error signal input corresponding to the difference between a desired control pressure and the actual head pressure.
Various modes of engine operation and various transients cause differences between desired control pressure and actual head pressure that change the magnitude of the error signal input to the closed-loop control. The error can also fluctuate both positively and negatively. Errors can range between relatively smaller ones and relatively larger ones. For example, certain transients in engine operation may cause relatively large error values, while other transients may cause only relatively small error values. Moreover, error changes may occur for reasons other than transients in engine operation and intentional changes in desired control pressure. Example of that are faults in sensors and/or processors.
In addition to increases in the magnitude of error, the durations of such increases can also have significance for proper pressure control. A smaller increase in error that has relatively longer duration may have as much significance as a larger increase of shorter duration.
In an engine that uses complex control technology, fault monitoring and logging are important for various reasons, including engine service, diagnostic testing, and compliance with applicable laws and regulations. It therefore becomes appropriate to monitor the head pressure of the hydraulic fluid that provides the pressure source for injection of fuel oil and to log certain faults that may be indicated in that pressure.